The present invention relates to the field of rotary blood pumps for assisting a failing human heart. More specifically, the present invention relates to the control of continuous flow rotary blood pump which does not compete with the bodies autonomic system unless the pump flow is detected to be outside of a predetermined range.
Various types of rotary blood pumps have been developed and are currently under development for use as heart assist devices. Compared to pulsatile pumps, rotary blood pumps have several advantages, including smaller size, higher efficiency, and a simpler design.
However, a servo control system for such rotary blood pumps has yet to be developed. Typically, operators have had to monitor patients in the intensive care unit in order to observe the condition of the pump and the patient, as manual intervention is currently required for controlling the rotational speed of the pump.
If such a rotary blood pump is to be used as a left ventricular assist device (LVAS), the pump flow should be increased when the pressurehead is decreased with the fixed rotational speed of the pump, because these parameters automatically adjust to the patient""s physiological condition, regardless of the fixed rotational speed of the pump impeller. However, when the venous return suddenly becomes too low because of physiological changes or overpumping, a high negative pressure may result at the inlet port of the pump, which may lead to a suction condition within the atrium and veins, which condition may result in serious injury or even death to the patient.
As rotary blood pumps may be used outside of a hospital environment, for example in nursing homes and home health care environments, it would be advantageous to provide an automated control system for controlling the rotary blood pump, without the need for human supervision and intervention. It would be advantageous for such a control system to operate the rotary blood pump automatically and effectively in response to any sudden changes in the operating conditions of the pump which deviate from a normal operating range.
The methods and apparatus of the present invention provide the foregoing and other advantages.
The present invention relates to a control system for a continuous flow rotary blood pump.
In an example embodiment, a normal operating range of the blood pump is established. The normal operating range may comprise a normal pump flow range and a normal pressure head range. A target rotational speed of the pump can then be set in accordance with the normal operating range. A current operating condition of the blood pump is determined. The current operating condition may comprise a current pump flow, a current pressure head, and a current rotational speed of the pump. The current operating condition can then be compared with the normal operating range. An appropriate control algorithm is then selected from a plurality of available control algorithms based on the comparison. The target rotational speed of the pump can then be adjusted using the selected control algorithm to maintain or recover the normal operating range.
The rotary blood pump may be used as a left ventricular assist device or a right ventricular assist device. The blood pump may be an implantable device or an external device.
Measurements of the current pump flow, the current pressure head, and the current rotational speed may be used to determine the current operating condition. The current pump flow, the current pressure head, and the current rotational speed may be measured by one or more sensors. Such sensors may be implantable sensors. Alternatively, such sensors may be external sensors.
The normal operating range may be established by determining a target operating point for the target rotational speed of the pump, which provides a target pump flow and a target pressure head. The normal pump flow range may be within a 20% deviation from the target pump flow. The normal pressure head range may be within a 25% deviation from the target pressure head.
During the normal operating range a normal operating condition control algorithm is selected. In such a case, the target rotational speed of the pump is maintained by applying proportional and derivative gain control to the pump. The proportional and derivative gain control may be applied in accordance with the formula:
u=Kp(Ytargetxe2x88x92Y)+Kd((d/dt)Ytargetxe2x88x92(d/dt)Y)
where u is a driving signal of the pump; Y is the rotational speed of the pump; Ytarget is the target rotational speed of the pump; Kp is the proportional gain; and Kd is the derivative gain. As an example, Kp may be set to approximately 0.02 and Kd may be set to approximately 0.05.
In the event that the current operating condition is above the normal operating range, a first abnormal operating condition control algorithm is selected. This algorithm decreases the target rotational speed until the normal operating range is recovered. For example, the target rotational speed may be decremented by x rpm every t seconds until the normal operating range is recovered. Research has shown that the normal operating range may be recovered by, for example, decrementing the rotational speed by approximately 150 rpm every 5 seconds.
In the event that the current operating condition is below the normal operating range, a second abnormal operating condition control algorithm is selected. This algorithm increases the target rotational speed until the normal operating range is recovered. For example, the target rotational speed may be incremented by x rpm every t seconds until the normal operating range is recovered. Research has shown that the normal operating range may be recovered by, for example, incrementing the rotational speed by approximately 150 rpm every 5 seconds.
However, when the normal operating range cannot be recovered by incrementing the rotational speed of the pump, is determined that a suction condition exists (e.g., due to overpumping). In the event of such a suction condition, a suction condition control algorithm is selected. This algorithm causes the suction condition to be released by continuously decreasing the target rotational speed of the pump to obtain a pump flow free from suction and free from overpumping. Once the suction condition is released, the target rotational speed of the pump is gradually increased to recover the normal operating range.
When releasing the suction condition, the target rotational speed may be continuously decremented by x1 rpm every t seconds. Once the suction condition is released, the target rotational speed may be continuously incremented by x2 rpm every t seconds to recover the normal operating condition.
Research has shown that the suction condition may be released when the rotational speed of the pump is decremented by approximately 150 rpm every 5 seconds (e.g., x1 is approximately 150 rpm and t is approximately 5). The normal operating range can then be recovered by incrementing the rotational speed of the pump by approximately 50 rpm every 5 seconds (e.g., x2 is approximately 50 rpm and t is approximately 5 seconds).
In an example embodiment of the invention, the pump may comprise a centrifugal pump having magnets implanted in the pump impeller. One or more Hall sensors may be used to detect the position of the pump impeller using the well-known Hall effect. The Hall sensors may be used to detect vertical and/or horizontal movement of the pump impeller. The rpm of the impeller may be adjusted based on the position as detected by the Hall sensors in order to maintain the impeller position in one of a top contact position or a dynamic suspension position. For example, where the Hall sensors detect the impeller position is at or near a bottom contact position, it is desirable to increase the impeller rpm so that the impeller position is moved towards a dynamic suspension position or a top contact position, as blood clots may form if the impeller remains in a bottom contact position.
Corresponding methods and apparatus are provided for controlling the continuous flow rotary blood pump in accordance with the invention.